It is not yet known if the properties of molecular gas in distant protocluster galaxies are significantly affected by their environment as galaxies are in local clusters. Through a deep, 64 h of ...effective on-source integration with the Australian Telescope Compact Array (ATCA), we discovered a massive, Mmol = 2.0 ± 0.2× 1011 M⊙, extended, ~40 kpc, CO(1–0)-emitting disk in the protocluster surrounding the radio galaxy, MRC 1138−262. The galaxy, at zCO = 2.1478, is a clumpy, massive disk galaxy, M∗ ~ 5 × 1011 M⊙, which lies 250 kpc in projection from MRC 1138−262 and is a known Hα emitter, named HAE229. This source has a molecular gas fraction of ~30%. The CO emission has a kinematic gradient along its major axis, centered on the highest surface brightness rest-frame optical emission, consistent with HAE229 being a rotating disk. Surprisingly, a significant fraction of the CO emission lies outside of the UV/optical emission. In spite of this, HAE229 follows the same relation between star-formation rate and molecular gas mass as normal field galaxies. HAE229 is the first CO(1–0) detection of an ordinary, star-forming galaxy in a protocluster. We compare a sample of cluster members at z > 0.4 thatare detected in low-order CO transitions, with a similar sample of sources drawn from the field. We confirm findings that the CO-luminosity and full-width at half maximum are correlated in starbursts and show that this relation is valid for normal high-z galaxies as well as for those in overdensities. We do not find a clear dichotomy in the integrated Schmidt-Kennicutt relation for protocluster and field galaxies. Our results suggest that environment does not have an impact on the “star-formation efficiency” or the molecular gas content of high-redshift galaxies. Not finding any environmental dependence in these characteristics, especially for such an extended CO disk, suggests that environmentally-specific processes such as ram pressure stripping do not operate efficiently in (proto)clusters.
Abstract
We present the “SINS/zC-SINF AO survey” of 35 star-forming galaxies, the largest sample with deep adaptive optics (AO)–assisted near-infrared integral field spectroscopy at
z
∼ 2. The ...observations, taken with SINFONI at the Very Large Telescope, resolve the H
α
and N
ii
emission and kinematics on scales of ∼1.5 kpc. The sample probes the massive (
M
⋆
∼ 2 × 10
9
− 3 × 10
11
M
⊙
), actively star-forming (SFR ∼ 10–600
M
⊙
yr
−1
) part of the
z
∼ 2 galaxy population over a wide range of colors ((
U
−
V
)
rest
∼ 0.15–1.5 mag) and half-light radii (
R
e,H
∼ 1–8.5 kpc). The sample overlaps largely with the “main sequence” of star-forming galaxies in the same redshift range to a similar
K
AB
= 23 mag limit; it has ∼0.3 dex higher median specific SFR, ∼0.1 mag bluer median (
U
−
V
)
rest
color, and ∼10% larger median rest-optical size. We describe the observations, data reduction, and extraction of basic flux and kinematic properties. With typically 3–4 times higher resolution and 4–5 times longer integrations (up to 23 hr) than the seeing-limited data sets of the same objects, the AO data reveal much more detail in morphology and kinematics. The complete AO observations confirm the majority of kinematically classified disks and the typically elevated disk velocity dispersions previously reported based on subsets of the data. We derive typically flat or slightly negative radial N
ii
/
gradients, with no significant trend with global galaxy properties, kinematic nature, or the presence of an AGN. Azimuthal variations in N
ii
/
are seen in several sources and are associated with ionized gas outflows and possibly more metal-poor star-forming clumps or small companions. The reduced AO data are made publicly available (
http://www.mpe.mpg.de/ir/SINS/SINS-zcSINF-data
).
We present results from a narrow-band survey of the field around the high-redshift radio galaxy MRC 2104−242. We have selected Hα emitters in a 7 arcmin2 field and compared the measured number ...density with that of a field sample at similar redshift. We find that MRC 2104−242 lies in an overdensity of galaxies that is 8.0 ± 0.8 times the average density of a blank field, suggesting it resides in a large-scale structure that may eventually collapse to form a massive cluster. We find that there is more dust obscured star formation in the protocluster galaxies than in similarly selected control field galaxies and there is tentative evidence of a higher fraction of starbursting galaxies in the denser environment. However, on average we do not find a difference between the star formation rate (SFR)–mass relations of the protocluster and field galaxies and so conclude that the SFR of these galaxies at z ∼ 2.5 is governed predominantly by galaxy mass and not the host environment. We also find that the stellar mass distribution of the protocluster galaxies is skewed towards higher masses and there is a significant lack of galaxies at M < 1010 M⊙ within our small field of view. Based on the level of overdensity we expect to find ∼22 star-forming galaxies below 1010 M⊙ in the protocluster and do not detect any. This lack of low-mass galaxies affects the level of overdensity which we detect. If we only consider high-mass (M > 1010.5 M⊙) galaxies, the density of the protocluster field increases to ∼55 times the control field density.
ABSTRACT
We present Very Large Telescope/Spectrograph for INtegral Field Observations in the Near Infrared (VLT/SINFONI) observations of 35 quasars at 2.1 < z < 3.2, the majority of which were ...selected from the Clusters Around Radio-Loud AGN (CARLA) survey. CARLA quasars have large C iv-based black hole masses (MBH > 109 M⊙) and powerful radio emission ($P_{500\, \rm MHz}$ > 27.5 W Hz−1). We estimate H α-based MBH, finding a scatter of 0.35 dex compared to C iv. We evaluate several recipes for correcting C iv-based masses, which reduce the scatter to 0.24 dex. The radio power of the radio-loud quasars is at most weakly correlated with the interconnected quantities H αwidth, L5100, and MBH, suggesting that it is governed by different physical processes. However, we do find a strong inverse correlation between C iv blueshift and radio power linked to higher Eddington ratios and L5100. Under standard assumptions, the black hole (BH) growth time is longer than the cosmic age for many CARLA quasars, suggesting that they must have experienced more efficient growth in the past. If these BHs were growing from seeds since the epoch of reionization, it is possible that they grew at the Eddington limit like the quasars at z ∼ 6–7, and then continued to grow at the reduced rates observed until z ∼ 2–3. Finally, we study the relation between MBH and environment, finding a weak positive correlation between MBH and galaxydensity measured by CARLA.
We report the detection of ubiquitous powerful nuclear outflows in massive (> or =, slanted10 super(11) M sub(middot in circle)) z ~ 2 star-forming galaxies (SFGs), which are plausibly driven by an ...active galactic nucleus (AGN). The sample consists of the eight most massive SFGs from our SINS/zC-SINF survey of galaxy kinematics with the imaging spectrometer SINFONI, six of which have sensitive high-resolution adaptive optics-assisted observations. All of the objects are disks hosting a significant stellar bulge. The spectra in their central regions exhibit a broad component in Halpha and forbidden NII and SII line emission, with typical velocity FWHM ~ 1500 km s super(-1), NII/Halpha ratio approximately 0.6, and intrinsic extent of 2-3 kpc. These properties are consistent with warm ionized gas outflows associated with Type 2 AGN, the presence of which is confirmed via independent diagnostics in half the galaxies. The data imply a median ionized gas mass outflow rate of ~60M yr super(-1) and mass loading of ~3. At larger radii, a weaker broad component is detected but with lower FWHM ~485 km s super(-1) and NII/Halpha approximately 0.35, characteristic for star formation-driven outflows as found in the lower-mass SINS/zC-SINF galaxies. The high inferred mass outflow rates and frequent occurrence suggest that the nuclear outflows efficiently expel gas out of the centers of the galaxies with high duty cycles and may thus contribute to the process of star formation quenching in massive galaxies. Larger samples at high masses will be crucial in confirming the importance and energetics of the nuclear outflow phenomenon and its connection to AGN activity and bulge growth.
We present APEX LABOCA 870 μm observations of the field around the high-redshift radio galaxy MRC1138−262 at z = 2.16. We detect 16 submillimeter galaxies (SMGs) in this ~140 arcmin2 bolometer map ...with flux densities in the range 3–11 mJy. The raw number counts indicate a density of SMGs that is up to four times that of blank field surveys. Based on an exquisite multiwavelength database, including VLA 1.4 GHz radio and infrared observations, we investigate whether these sources are members of the protocluster structure at z ≈ 2.2. Using Herschel PACS and SPIRE and Spitzer MIPS photometry, we derive reliable far-infrared (FIR) photometric redshifts for all sources. Follow-up VLT ISAAC and SINFONI NIR spectra confirm that four of these SMGs have redshifts of z ≈ 2.2. We also present evidence that another SMG in this field, detected earlier at 850 μm, has a counterpart that exhibits Hα and CO(1–0) emission at z = 2.15. Including the radio galaxy and two SMGs with FIR photometric redshifts at z = 2.2, we conclude that at least eight submm sources are part of the protocluster at z = 2.16 associated with the radio galaxy MRC1138−262. We measure a star formation rate density SFRD ~1500 M⊙ yr-1 Mpc-3, four magnitudes higher than the global SFRD of blank fields at this redshift. Strikingly, these eight sources are concentrated within a region of 2 Mpc (the typical size of clusters in the local universe) and are distributed within the filaments traced by the HAEs at z ≈ 2.2. This concentration of massive, dusty starbursts is not centered on the submillimeter-bright radio galaxy which could support the infalling of these sources into the cluster center. Approximately half (6/11) of the SMGs that are covered by the Hα imaging data are associated with HAEs, demonstrating the potential of tracing SMG counterparts with this population. To summarize, our results demonstrate that submillimeter observations may enable us to study (proto)clusters of massive, dusty starbursts.
We present the results of a large program conducted with the Very Large Telescope and augmented by observations with the Keck telescope to search for forming clusters of galaxies near powerful radio ...galaxies at 2.0 < z < 5.2. Besides MRC 1138-262 at z = 2.16, the radio galaxy observed in our pilot program, we obtained narrow- and broad-band images of eight radio galaxies and their surroundings. The imaging was used to select candidate Ly\alpha emitting galaxies in 3\times3 Mpc super(2) areas near the radio galaxies. A total of 300 candidate emitters were found with a rest-frame Ly\alpha equivalent width of EW sub(0) > 15 Aa and significance 3$--> \Sigma \equiv {\it EW}_0/\Delta {\it EW}_0 > 3. Follow-up spectroscopy was performed on 152 candidates in seven of the radio galaxy fields. Of these, 139 were confirmed to be Ly\alpha emitters, four were low redshift interlopers and nine were non-detections. With the adopted criteria the success rate is 139/152 = 91%. In addition, 14 objects with EW sub(0) < 15 and/or \Sigma < 3 were confirmed to be Ly\alpha emitters. Combined with the 15 Ly\alpha emitters near MRC 1138-262, we have determined Ly\alpha redshifts for 168 objects near eight radio galaxies. At least six of our eight fields are overdense in Ly\alpha emitters by a factor 3-5 as compared to the field density of Ly\alpha emitters at similar redshifts, although the statistics in our highest redshift field ( z = 5.2) are poor. Also, the emitters show significant clustering in velocity space. In the overdense fields, the width of the velocity distributions of the emitters is a factor 2-5 smaller than the width of the narrow-band filters. Taken together, we conclude that we have discovered six forming clusters of galaxies (protoclusters). We estimate that roughly 75% of powerful ( 10 logical and --> L_\mathrm > 10erg s super(-1) Hz super(-1) sr super(-1)) high redshift radio galaxies reside in a protocluster. The protoclusters have sizes of at least 1.75 Mpc, which is consistent with the structure sizes found by other groups. By using the volume occupied by the overdensities and assuming a bias parameter of b =3-6, we estimate that the protoclusters have masses in the range 2{-}9 \times 10M_{\odot}. These protoclusters are likely to be progenitors of present-day (massive) clusters of galaxies. For the first time, we have been able to estimate the velocity dispersion of cluster progenitors from z\sim5 to similar to 2. The velocity dispersion of the emitters increases with cosmic time, in agreement with the dark matter velocity dispersion in numerical simulations of forming massive clusters.
Observations of the radio galaxy MRC 0316–257 at $z = 3.13$ and the surrounding field are presented. Using narrow- and broad-band imaging obtained with the VLT, 77 candidate Lyα emitters with a ...rest-frame equivalent width of >15 Å were selected in a ∼7´$\,\times\,7$´ field around the radio galaxy. Spectroscopy of 40 candidate emitters resulted in the discovery of 33 emission line galaxies of which 31 are Lyα emitters with redshifts similar to that of the radio galaxy, while the remaining two galaxies turned out to be $\ion{O}{ii}$ emitters. The Lyα profiles have widths (FWHM) in the range of 120–800 km s-1, with a median of 260 km s-1. Where the signal-to-noise was large enough, the Lyα profiles were found to be asymmetric, with apparent absorption troughs blueward of the profile peaks, indicative of absorption along the line of sight of an $\ion{H}{i}$ mass of at least $2 \times 10^2 {-} 5 \times 10^4$ M$_{\odot}$. Besides that of the radio galaxy and one of the emitters that is a QSO, the continuum of the emitters is faint, with luminosities ranging from 1.3 L* to <0.03 L*. The colors of the confirmed emitters are, on average, very blue. The median UV continuum slope is $\beta = -1.76$, bluer than the average slope of LBGs with Lyα emission ($\beta \sim -1.09$). A large fraction of the confirmed emitters (∼2/3) have colors consistent with that of dust-free starburst galaxies. Observations with the Advanced Camera for Surveys on the Hubble Space Telescope show that the emitters that were detected in the ACS image have a range of different morphologies. Four Lyα emitters (∼25%) were unresolved with upper limits on their half light radii of $r_{\rm h} < 0.6-1.3$ kpc, three objects (∼19%) show multiple clumps of emission, as does the radio galaxy, and the rest (∼56%) are single, resolved objects with $r_{\rm h} < 1.5$ kpc. A comparison with the sizes of Lyman break galaxies at $z \sim 3$ suggests that the Lyα emitters are on average smaller than LBGs. The average star formation rate of the Lyα emitters is 2.6 M$_{\odot}\;{\rm yr}^{-1}$ as measured by the Lyα emission line or <3.9 M$_{\odot}\;{\rm yr}^{-1}$ as measured by the UV continuum. The properties of the Lyα galaxies (faint, blue and small) are consistent with young star forming galaxies which are still nearly dust free. The volume density of Lyα emitting galaxies in the field around MRC 0316–257 is a factor of $3.3^{+0.5}_{-0.4}$ larger compared with the density of field Lyα emitters at that redshift. The velocity distribution of the spectroscopically confirmed emitters has a dispersion of 640 km s-1, corresponding to a FWHM of 1510 km s-1, which is substantially smaller than the width of the narrow-band filter (${\it FWHM} \sim 3500$ km s-1). The peak of the velocity distribution is located within 200 km s-1 of the redshift of the radio galaxy. We conclude that the confirmed Lyα emitters are members of a protocluster of galaxies at $z \sim 3.13$. The size of the protocluster is unconstrained and is larger than $3.3 \times 3.3$ Mpc2. The mass of this structure is estimated to be >$3{-}6 \times 10^{14}$ M$_{\odot}$ and could be the progenitor of a cluster of galaxies similar to e.g. the Virgo cluster.
We present deep HST ACS observations in unk toward the z = 4.1 radio galaxy TN J1338-1942 and its overdensity of >30 spectroscopically confirmed Ly alpha emitters (LAEs). We select 66 g sub(475) band ...dropouts to unk = 27, 6 of which are also LAEs. Although our color-color selection results in a relatively broad redshift range centered on z - 4.1, the field of TN J1338-1942 is richer than the average field at the >5 sigma significance, based on a comparison with GOODS. The angular distribution is filamentary with about half of the objects clustered near the radio galaxy, and a small, excess signal (2 sigma ) in the projected pair counts at separations of theta < 10" is interpreted as being due to physical pairs. The LAEs are young (a few times 10 super(7) yr), small ((r sub(bl)) unk 0.13") galaxies, and we derive a mean stellar mass of similar to 10 super(8)-10 super(9) M unk based on a stacked K sub(s) band image. We determine star formation rates, sizes, morphologies, and color-magnitude relations of the g sub(475) -dropouts and find no evidence for a difference between galaxies near TN J1338-1942 and in the field. We conclude that environmental trends as observed in clusters at much lower redshift are either not yet present or washed out by the relatively broad selection in redshift. The large galaxy overdensity, its corresponding mass overdensity, and the subclustering at the approximate redshift of TN J1338-1942 suggest the assemblage of a >10 super(14) M unk structure, confirming that it is possible to find and study cluster progenitors in the linear regime at z unk 4.
PDF
